In an optical disk representative of a magnetic disc driver (hereinafter, referred to as “HDD: hard disk drive”), a CD (compact disc), and a DVD (digital versatile disc), or a radio communication mobile terminal, a phase locked loop is used in generation of a clock signal for operating a logical circuit. It is general that the phase locked loop is constituted as a semiconductor integrated circuit device together with a peripheral circuit. In recent years, the operating speed of those information devices is remarkably higher, and the operating frequency of the phase locked loop reaches the GHz band.
As an example of the phase locked loop having a high speed operation which is suitable for a structure of the semiconductor integrated circuit device, for example, patent document #1: Japanese Patent Laid-open No. H11-298302 and patent document #2: Japanese Patent Laid-open No. 2001-358565 disclose an example in which a frequency variable oscillator circuit that is one of the main structural circuits is made up of an oscillator circuit in which delay circuits that change the amount of delay according to a current are annularly connected at a multistage.
Also, in a digital signal analysis device, an inputted digital signal is liable to lower the amplitude or to change the DC level, that is, to produce the DC offset as the frequency becomes higher. Patent document #3: Japanese Patent Laid-open No. H5-7135 discloses an example of a correction circuit that shapes the waveform of the above digital signal to correct the amplitude change and the DC offset.